Begin by washing the fish in cold water and drying them with kitchen paper.
Then warm a large frying pan (10 inches/25.5 cm) over a gentle heat, crush the peppercorns, coriander and fennel seeds in a mortar, add the crushed spices to the frying pan and let them dry-roast for about 1 minute to draw out the flavours. Then add the olive oil, garlic and onion and let them cook gently for about 5 minutes or until the onion is pale gold.
Next add the tomatoes (you can also watch how to skin tomatoes by clicking on the Cookery School Video on this page), lemon juice, wine vinegar and white wine, stir and, when it begins to bubble, season with salt and pepper and add the oregano. Now add the sliced fennel to the pan, followed by the trout, basting the fish with the juices. Put a timer on and give the whole thing 10 minutes' gentle simmering.
After that, use a fish slice and fork to turn each fish over carefully on to its other side – don't prod it or anything like that, or the flesh will break. Then give it another 10 minutes' cooking on the other side. Gently remove the trout to a shallow serving dish, spoon the sauce all over, cool, cover with clingfilm and leave them in a cool place.
If you want to make this dish the day before, that's okay, provided you keep it in the fridge and remove it an hour before serving. Either way, sprinkle each trout with the garnish (made by simply combining all the ingredients together) before taking them to the table.